Microwave assisted magnetic recording drive utilizing interlaced track recording

ABSTRACT

Bottom tracks are written to a recording medium using a first setting of a microwave assisted magnetic recording (MAMR) head. Top tracks are interlaced between and partially overlapping the bottom tracks using a second setting of the MAMR head, the second setting resulting in a narrower track width than the first setting.

SUMMARY

Various embodiments described herein are generally directed to amicrowave assisted magnetic recording drive utilizing interlaced trackrecording. In one embodiment, bottom tracks are written to a recordingmedium using a first setting of a microwave assisted magnetic recording(MAMR) head. Top tracks are interlaced between and partially overlappingthe bottom tracks using a second setting of the MAMR head, the secondsetting resulting in a narrower track width than the first setting.

In another embodiment, bottom tracks are written to a recording mediumusing a first microwave power of a MAMR head and a first linear bitdensity. The first microwave power results in a first track width of thebottom tracks. Top tracks are written interlaced between and partiallyoverlapping the bottom tracks using a second microwave power of the MAMRhead and a second linear bit density. The second microwave power islower than the first microwave power and results in a second track widthless than the first track width. These and other features and aspects ofvarious embodiments may be understood in view of the following detaileddiscussion and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The discussion below makes reference to the following figures, whereinthe same reference number may be used to identify the similar/samecomponent in multiple figures.

FIG. 1 is a diagram illustrating a magnetic recording device accordingto an example embodiment;

FIG. 2 is a diagram illustrating interlaced magnetic recording tracksaccording to an example embodiment;

FIG. 3 is a block diagram illustrating interlaced and shingled tracksaccording to an example embodiment;

FIG. 4 is a block diagram illustrating a recording schemed according toan example embodiment;

FIGS. 5 and 6 are flowcharts illustrating a procedure according to anexample embodiment;

FIG. 7 is a block diagram of an apparatus according to an exampleembodiment; and

FIG. 8 is a flowchart of a method according to an example embodiment.

DETAILED DESCRIPTION

The present disclosure generally relates to data storage devices thatutilize magnetic storage media, e.g., disks. Recording schemes have beendeveloped to increase areal density for conventional magnetic recording(CMR) devices, e.g., perpendicular magnetic recording (PMR) as well asdevices using newer technologies, such as heat-assisted magneticrecording (HAMR), microwave-assisted magnetic recording (MAMR). One ofthese recording schemes is interlaced magnetic recording (IMR), whichgenerally involves writing some tracks that partially overlap previouslywritten tracks. This allows writing the tracks at a narrower width thanwould be possible in conventional recording schemes, where tracks arespaced apart to prevent crosstrack interference. While IMR-recordedtracks cannot be randomly updated as easily as conventionally-recordedtracks, the drive architecture can be adapted to minimize the effects onrandom writes.

In a disk drive utilizing interleaved magnetic recording (IMR), thereare two types of data tracks written. The first is a bottom track, whichis generally written at higher linear density using a wider write head,or using a write configuration that results in a wider track beingwritten. The second is a top track, which is generally written at lowerlinear density using a narrower write head, or using a writeconfiguration that results in a wider track being written. The bottomtracks are written first, with a relatively wide spacing between, andthen the top tracks are written in the spacing between adjacent toptracks. The intent of writing the top tracks is to encroach enough onthe adjacent bottom tracks to partially overwrite the bottom trackedges. Because these track edges tend to have poorer SNR than the middleof the track, overwriting the edges has a minor impact on the overallbottom track SNR.

The different characteristics of the top and bottom IMR tracks cancomplicate writing the data from those tracks. The top and bottom trackswill usually have different characteristics, including track width,linear bit-density, signal-to-noise ratio, etc. Typically, aconventional write pole will not significantly increase write width(which defines track width) in response to changes in write currentapplied to a write coil that magnetizes the pole. Therefore, IMRrecording that utilizes conventional recording heads (e.g., PMR writer)may use strategies such as two or more writers with different widths towrite top and bottom tracks.

In order to reduce costs and complexity, it is desirable to have asingle write transducer that can write both top and bottom tracks in anIMR drive. In embodiments described below, a MAMR write transducer isused to write tracks having different width and other characteristics.Such a transducer can be used to write the top and bottom tracks for IMRwith a single head, and may have other uses. For example, in some casesa drive may be configured to write data with different bit-aspect ratios(BAR) in different regions of the drive. This may be used to maximizestorage space, increase performance, customize performance for end-userspecification, etc. Being able to write at significantly different trackwidths via MAMR allows a wider range of BAR to be used.

In FIG. 1, a block diagram shows a side view of a read/write head 102(also referred to as a “read head,” “write head,” “recording head,”etc.) according to an example embodiment. The read/write head 102 mayalso be referred to herein as a write head, read head, recording head,etc. The read/write head 102 is part of slider that is coupled to an arm104 by way of a suspension 106, e.g., a gimbal. The read/write head 102includes read/write transducers 108 at a trailing edge that are heldproximate to a surface 110 of a magnetic recording medium 111, e.g., amagnetic disk. When the read/write head 102 is located over surface 110of recording medium 111, a flying height 112 is maintained between theread/write head 102 and the surface 110 by a downward force of arm 104.This downward force is counterbalanced by an air cushion that existsbetween the surface 110 and an air bearing surface (ABS) 103 (alsoreferred to herein as a “media-facing surface”) of the read/write head102 when the recording medium 111 is rotating.

In order to provide control of the clearance between the read/writetransducers 108 and the recording medium 111, one or more clearanceactuators 114 (e.g., heaters) are formed in the read/write head 102. Acurrent applied to the heater 114 induces a local protrusion whichvaries the clearance. The amount of current applied to the heater 114may vary based on which of the read/write transducers 108 are in use,and may also be adjusted to account for irregularities in the mediasurface 110, changes in ambient temperature, location of the read/writehead 102 over the medium 111, etc.

A controller 118 is coupled to the read/write transducers 108, as wellas other components of the read/write head 102, such as heaters 114,sensors, etc. The controller 118 may be part of general- orspecial-purpose logic circuitry that controls the functions of a storagedevice that includes at least the read/write head 102 and recordingmedium 111. The controller 118 may include or be coupled to a read/writechannel 119 that include circuits such as preamplifiers, buffers,filters, digital-to-analog converters, analog-to-digital converters,decoders, encoders, etc., that facilitate electrically coupling thelogic of the controller 118 to the signals used by the read/write head102 and other components.

The illustrated read/write head 102 may be configured as a MAMR device,and so includes additional components that assist the read/writetransducer 108. A spin-torque oscillator (STO) 122 used with theread/write transducer 108 which, together with a magnetic write pole,generates a powerful but localized magnetic field. This increases themagnetic field over what can be provided by the write pole itself. Assuch, a recording medium with higher magnetic coercivity can be usedcompared with conventional recording media, thereby allowing reliablestorage of bits in a smaller area on the medium compared to conventionalmedia.

The read/write transducer 108 of the read/write head 102 includes one ormore read elements, such as a magneto-resistive stack. The read elementsare used to form an electrical signal that varies with changes inmagnetic field on the recording medium 111. For example, amagneto-resistive element will change resistance in response to changesin local magnetic field. A current passing through the element will varybased on the changes in resistance.

In FIG. 2, a block diagram illustrates IMR tracks according to anexample embodiment. In this IMR process, bottom tracks 200-202 are firstwritten the recording medium using a bottom track width 203 and atbottom track pitch 210. Top tracks 204, 205 are then written partiallyoverlapping between respective bottom tracks 200-202, and therefore areinterlaced between the bottom tracks 200-202. The top tracks are writtenat a top track width 206 and at top track pitch 208. Note that thetracks 200-202, 204 and 205 are not multi-level, and the illustratedstacking of tracks is for purposes of explanation and not intended to bea physical representation of IMR tracks.

Because the bottom tracks 200-202 are written at a relatively largecross-track separation from one another, the bottom tracks 200-202 canbe written using a relatively larger width 203 than the top tracks 204,205 without risk of adjacent track erasure. The larger width 203 enablesrecording the bottom tracks 200-202 at relatively higher linear bitdensity than that of the top tracks 204, 205. For a HAMR device, thedifferent widths 203, 206 can be achieved by varying laser power to varythe size of the hotspot in the recording medium. The width and linearbit density of the top and bottom tracks 204, 205, 200-202 define thebit-aspect ratio (BAR) of the respective tracks.

Because individual recording heads and media will have differentcharacteristics due to manufacturing tolerances, each drive may havedifferent top and bottom BAR values that are optimum. In some cases, BARmay be different for different disk surfaces within a drive, anddifferent for different zones within a disk surface. For example, in aMAMR drive, a selected combination of STO power, STO frequency, writecoil power, and linear bit density (which can be controlled by a clockthat defines bit transitions) can produce a selected BAR for aparticular recording regions. Because the STO effect on track width willalso have an effect on adjacent track spacing, the value of trackspacing may also be defined together with the selected BAR. Thecombination of linear bit density and track spacing defines the arealdensity (ADC) for the region being considered.

Writing IMR with MAMR can be relatively straightforward because thetrack width can be adjusted with a combination of settings that includemicrowave power, microwave frequency, and write coil power. The bottomtracks 201-203 can be written wide and support a high linear densityusing a high microwave power and higher write coil power. The top tracks204, 205 can be written narrow with lower microwave power and lowerwrite coil power. The effect of microwave frequency on the track widthcan be determined and tuned for particular combinations of heads andmedia. Also note that in some cases, the microwave power may be zero,such that the head is operating in a CMR mode for one set of the tracks.Bottom tracks experience double sided squeeze by the two adjacent toptracks whereas top tracks are non-squeezed since the neighboring toptracks are two tracks away. Since the top tracks are the only source ofencroachment, the top track write triple and microwave power may definedefines the track pitch of the entire MAMR IMR system.

The ADC gain for MAMR IMR is from at least three sources. First, bottomtrack linear density can increase due to increased microwave power.Second, the top track linear density gains from the non-squeezedconditions. Generally, the top tracks do not suffer from adjacent trackwrite interference since the next top track is two tracks away. Third,the track pitch is defined by the top track write current and microwavepower which can be lower than MAMR CMR and gives a narrower track,thereby enabling high track density.

One complication in using IMR relates to the order that tracks arewritten. Top tracks can be re-written as many times as needed but tooverwrite a bottom track with top tracks present, the adjacent toptracks may need to be read and then re-written after the bottom track iswritten. A shingled magnetic recording (SMR) arrangement has similarissues, in that updating a bottom track may require reading andrewriting any tracks that overlap the bottom track.

One way to deal with track writing order is to group top tracks andbottom tracks into different logical bands. The system performancepenalty for IMR will be similar or less than SMR because there are atmost two tracks that overlap a bottom track. For SMR, there may be morethan two sequentially-written and overlapping tracks that need to berewritten in response to updating a bottom track. The workload of thedrive and the architecture may also favor IMR, e.g., in cases wherecertain types of data (e.g., write-once, read-many) can be placed inbottom tracks to reduce impact on system performance.

There may be other drive architecture advantages to MAMR IMR over MAMRSMR related to drive performance. The MAMR SMR ADC gains are mostly intrack pitch while the MAMR IMR ADC gains are in linear bit density. Thismeans that MAMR IMR can increase data rate over MAMR SMR. The lineardensity gain of the bottom track in MAMR IMR is not achievable with MAMRSMR, even if large microwave powers are used since IMR uses the straighttrimmed track center whereas MAMR SMR uses the curved track edge. Thisis shown by the block diagram in FIG. 3, which shows IMR and SMR tracksthat may be written by a device according to an example embodiment.

Shingled tracks 300-302 are shown on the left of the figure. The SMRtracks are shown written from left to right, with track 300 writtenfirst, track 301 written next partially overlapping track 300 and track301, and finally track 302 written partially overlapping track 301.Because track 301 both overlaps and is overlapped, it is indicated asbeing both a top and bottom track for purposes of this discussion. Aread transducer 304 is shown centered over track 301. Interlaced tracks310-312 are shown on the right side of the figure. Bottom track 311 iswritten first, followed by top tracks 310, 312 that are interlaced withand partially overlap edges of the bottom track 311. Read transducer 314is shown over bottom track 311. Note that for bottom SMR tracks 300,301, the reader 304 will be centered over a region somewhat to the leftof the originally written track center, whereas for the bottom IMR trackthe reader 314 is centered over the originally written bottom trackcenter. This enables the IMR bottom tracks to yield better signal for agiven track width and linear bit density.

An IMR drive can include features to reduce the impact of thewrite-order dependence of the bottom tracks. In FIG. 4, a block diagramshows a MAMR IMR track arrangement according to an example embodiment.The tracks are separated into at least two different groups 400, 402,labeled as bottom and top tracks. Each bottom track is next to toptracks and each bottom track is next to top tracks as seen in block 404,where the groups of tracks 400, 402 are shown written to a portion ofthe disk. However, the tracks within each group 400, 402 may be treatedas adjacent tracks during reading and writing.

For example, as indicated by block 406, the bottom tracks 400 may beassigned a first logical block address (LBA) range that is continuousacross some or all of the bottom tracks. Similarly, as shown in block408, the top tracks 402 may be assigned a second LBA range that iscontinuous across some or all of the top tracks. In this way, thedifferent LBA ranges 406, 408 may be used for different types of data(e.g., sequential, random, write-once-read-many, etc.) that minimizesimpact on the additional steps used to update bottom tracks 400.Generally, more active data (e.g., random data) will be targeted to thetop tracks 402, and more static data (e.g., sequential data) will betargeted to the bottom tracks 400.

In order to find an optimum value of the density of the tracks, thebottom tracks 400 may be written first to determine the highest lineardensity possible for this track with the optimized write currentparameters and microwave power. Then linear density is reduced such thatthe on-track bit error rate (BER) has a small BER margin (such as 0.3decade, for example). The purpose of this BER margin is to assure thebottom tracks 400 have adequate BER after the top tracks are written.Then the top tracks 402 are written using the same head but at adifferent optimized write current and microwave power.

When the bottom tracks 400 are written, there are no adjacent tracks andtherefore no adjacent track interference (ATI), and the writer can beoptimized to boost linear density. For example, higher microwave power,higher steady state write currents or write current overshoots can beused for the bottom track. When the top tracks 402 are written, thebottom tracks 400 will be trimmed by the top tracks 402, but informationat the center of the bottom tracks 400 will remain. The data on the toptracks 402 in principle has higher ADC since it is not necessary toprovision for ATI margin.

In FIG. 5, a flowchart shows a track calibration procedure according toan example embodiment. This procedure may be performed in a factoryenvironment, e.g., drive calibration, and may also be performed in thefield, e.g., user configuration or re-configuration of the drive. Theprocess involves setting 500 a starting linear density for bottomtracks. Bottom tracks (e.g., separated tracks at a bottom-to-bottomtrack pitch) are written 501 at this density and read back 502 todetermine BER of the tracks. If it is determined at block 503 that theBER is below a maximum value (e.g., as specified by drive performancetarget), then the linear bit density is increased 504, and the writing501 and reading 503 are repeated until block 503 returns ‘yes.’

When block 503 returns ‘yes,’ the maximum linear bit density has beenfound for the bottom tracks, and may be recorded 505 for futurereference. Thereafter, another iteration is performed that involvesreducing 506 the linear bit density, writing 507 and reading 508 trackssimilar to before. In this case, the BER is tested 509 to determine ifit is above a threshold. The threshold is predefined and generally lowerthan the maximum allowable BER. Once the BER is at or below thisthreshold, block 509 returns ‘no’ and the bottom track linear density isrecorded 510 to be used in drive operation. Thereafter the procedurecontinues as shown in FIG. 6.

In FIG. 6, a starting top track linear bit density is set 600, anditerations of writing and reading at increasing linear bit densities ofthe top track is performed as indicated by blocks 600-604. This is usedto obtain a maximum top track linear bit density, which is recorded 605and may be used during operation of the drive together with the bottomtrack density that was shown being obtained in FIG. 5. After obtainingthe top track linear bit density, one or more bottom tracks that areoverwritten by top tracks (e.g., tracks written at block 601) are read606 to find if the BER has changed past some delta over the previousthreshold. If the BER has gone past this delta as indicated at block607, then the linear density of the bottom tracks may be adjusted (e.g.,decreased) 608 to compensate. Other changes may be made instead of or inaddition to this adjustment 608. For example, track width of the toptracks may be adjusted (e.g., decreased) along with a correspondingchange (e.g., decrease) in top track linear bit density.

In FIG. 7, a diagram illustrates components of a storage drive apparatus700 that utilizes one or more read/write heads 712 according to exampleembodiments. The apparatus includes circuitry 702 such as a systemcontroller 704 that processes read and write commands and associateddata from a host device 706. The host device 706 may include anyelectronic device that can be communicatively coupled to store andretrieve data from a data storage device, e.g., a computer. The systemcontroller 704 is coupled to a read/write channel 708 that reads fromand writes to surfaces of one or more magnetic disks 710.

The read/write channel 708 generally converts data between the digitalsignals processed by the system controller 704. The read/write head 712includes at least one write transducer and a read transducer, and atleast one of the heads 712 is configured as a MAMR read/write head. Theread/write channel 708 may include analog and digital circuitry such asdecoders, timing-correction units, error correction units, etc. Theread/write channel is coupled to the heads via interface circuitry 713that may include preamplifiers, filters, digital-to-analog converters,analog-to-digital converters, etc. The read/write channel 708 includescircuitry to activate a STO integrated in the MAMR head 712 duringrecording to the disk 710.

The read/write channel 708 may have particular features that facilitateIMR reading and writing. For example, different channel configurations(e.g., parameters for write signals, decoding, timing correction, errorcorrection, etc.) may be used depending on whether a top or bottom trackis currently being written/read. The read/write channel 708 may beconfigured to read and write data differently for different zones ofdisk 710. For example, some zones may use different writing formats suchas SMR, IMR, and conventional tracks.

In addition to processing user data, the read/write channel 708 readsservo data from servo wedges 714 on the magnetic disk 710 via theread/write head. All of the multiple readers of the read/write head maybe used to read servo data, or only a subset thereof. The servo data aresent to a servo controller 716, which uses the data to provide positioncontrol signals 717 to a VCM 718. The VCM 718 rotates an arm 720 uponwhich the read/write heads 712 are mounted in response to the controlsignals 717. The position control signals 717 may also be sent tomicroactuators 724 that individually control each of the read/writeheads 712, e.g., causing small displacements at each head.

An IMR track recording module 730 is stored in memory 711 and isoperable to set different recording parameters via the read/writechannel 708 when recording different top and bottom tracks. For example,bottom tracks are written to the disk recording medium using a firstsetting of the MAMR head 712, then top tracks are written interlacedbetween and partially overlapping the bottom tracks using a secondsetting of the MAMR head. The second setting resulting in the top tracksbeing narrower than the bottom tracks written using the first setting.The first and second settings may include different combinations ofwrite coil power, spin-torque oscillator power, and spin-torqueoscillator frequency. Note that in this context, only one of write coilpower, spin-torque oscillator power, and spin-torque oscillatorfrequency need be different for the combinations to be different. Alsonote that the powers may refer dynamic characteristics of current orvoltage applied to the write pole and/or spin-torque oscillator, such assteady-state power, rise time, overshoot, etc.

In reference now to FIG. 8, a flowchart illustrates a method accordingto an example embodiment. The method involves writing 800 bottom tracksto a recording medium using a first setting of a MAMR head. Top tracksare written 801 interlaced between and partially overlapping the bottomtracks using a second setting of the MAMR head. The second settingresults in a narrower track width than the first setting. The methodoptionally involves reading 802 the top and bottom tracks via one ormore read transducers of the MAMR head. For example, the head may havenarrower are wider read transducers that are each optimized to read oneof the top and bottom tracks.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

The various embodiments described above may be implemented usingcircuitry, firmware, and/or software modules that interact to provideparticular results. One of skill in the arts can readily implement suchdescribed functionality, either at a modular level or as a whole, usingknowledge generally known in the art. For example, the flowcharts andcontrol diagrams illustrated herein may be used to createcomputer-readable instructions/code for execution by a processor. Suchinstructions may be stored on a non-transitory computer-readable mediumand transferred to the processor for execution as is known in the art.The structures and procedures shown above are only a representativeexample of embodiments that can be used to provide the functionsdescribed hereinabove.

The foregoing description of the example embodiments has been presentedfor the purposes of illustration and description, and is not intended tobe exhaustive or to limit the invention to the precise form disclosed.Many modifications and variations are possible in light of the aboveteaching. Any or all features of the disclosed embodiments can beapplied individually or in any combination are not meant to be limiting,but purely illustrative. It is intended that the scope of the inventionbe limited not with this detailed description, but rather determined bythe claims appended hereto.

What is claimed is:
 1. A method, comprising: writing bottom tracks to arecording medium using a first setting of a spin-torque oscillator of amicrowave assisted magnetic recording (MAMR) head; writing top tracksinterlaced between and partially overlapping the bottom tracks using asecond setting of the spin-torque oscillator, the second settingresulting in a narrower track width than the first setting.
 2. Themethod of claim 1, wherein the first and second settings comprise firstand second microwave powers of the spin-torque oscillator.
 3. The methodof claim 1, wherein for one of the first and second settings, no poweris applied to the spin-torque oscillator and for another of the firstand second settings a non-zero power is applied to the spin-torqueoscillator.
 4. The method of claim 1, wherein the first and secondsettings comprise first and second different combinations of write coilpower, spin-torque oscillator power, and spin-torque oscillatorfrequency.
 5. The method of claim 1, wherein the bottom and top tracksare written at different linear bit densities.
 6. The method of claim 1,wherein the bottom tracks are assigned to a first logical group and thetop tracks are assigned to a second logical band, tracks within thefirst and second logical bands being treated as adjacent tracks duringreading and writing.
 7. The method of claim 6, wherein the first andsecond groups have respective first and second continuous logical blockaddress ranges.
 8. The method of claim 6, wherein static data istargeted for the first group and active data is targeted for the secondgroup.
 9. The method of claim 1, further comprising, before writing thetop and bottom tracks, performing a procedure to determine a targetlinear bit density of the bottom tracks, the procedure comprising:writing first bottom test tracks at increasing linear bit densitiesuntil a maximum allowable bit error rate is measured; determining amaximum linear bit density associated with the maximum allowable biterror rate; starting with the maximum linear bit density, writing secondbottom test tracks at decreasing linear bit densities until a thresholdbit error rate is determined; and setting the target linear bit densityof the bottom tracks based on a linear bit density corresponding to thethreshold bit error rate.
 10. The method of claim 9, wherein theprocedure further comprises: writing top test tracks at increasinglinear bit densities until a second maximum bit error rate is measuredat a target linear bit density of the top tracks; if writing the toptracks at the target linear bit density partially overlapping the bottomtracks does not increase the threshold bit error rate of the bottomtracks beyond a threshold, using the target linear bit density of thetop tracks to write the top tracks, otherwise using a reduced linear hitdensity less than he target linear bit density of the top tracks towrite the top tracks.
 11. An apparatus, comprising: interface circuitryoperable to control a spin-torque oscillator of a microwave assistedmagnetic recording (MAMR) head; and a controller coupled to theinterface circuitry, the controller configured to: write bottom tracksto a recording medium of the apparatus using a first setting of thespin-torque oscillator; write top tracks interlaced between andpartially overlapping the bottom tracks using a second setting of thespin-torque oscillator, the second setting resulting in a narrower trackwidth than the first setting.
 12. The apparatus of claim 11, wherein thefirst and second settings comprise first and second microwave powers ofthe spin-torque oscillator.
 13. The apparatus of claim 11, wherein forone of the first and second settings, no power is applied to the spintorque oscillator and for another of the first and second settings anon-zero power is applied to the spin-torque oscillator.
 14. Theapparatus of claim 11, the method of claim 1, wherein the first andsecond settings comprise first and second different combinations ofwrite coil power, spin-torque oscillator power, and spin-torqueoscillator frequency.
 15. The apparatus of claim 11, wherein the bottomand top tracks are written at different linear bit densities.
 16. Theapparatus of claim 11, wherein the bottom tracks are assigned to a firstlogical group and the top tracks are assigned to a second logical band,tracks within the first and second logical bands being treated asadjacent tracks during reading and writing.
 17. The apparatus of claim16, wherein the first and second groups have respective first and secondcontinuous logical block address ranges.
 18. The apparatus of claim 16,wherein static data is targeted r the first group and active data istargeted for the second group.
 19. A method, comprising: writing bottomtracks to a recording medium using a first microwave power of aspin-torque oscillator of a microwave assisted magnetic recording (MAMR)head and a first linear bit density, the first microwave power resultingin a first track width of the bottom tracks; and writing top tracksinterlaced between and partially overlapping the bottom tracks using asecond microwave power of the spin-torque oscillator and a second linearbit density, the second microwave power being lower than the firstmicrowave power and resulting in a second track width less than thefirst track width.
 20. The method of claim 19, wherein the bottom tracksare assigned to a first logical group and the top tracks are assigned toa second logical band, tracks within the first and second logical bandsbeing treated as adjacent tracks during reading and writing.